Illegal intrusion and burglary is a threat to nearly all property owners or occupiers. Therefore, the alarm systems are being installed in increasing numbers all over the world. Many building entrances, such as windows and doors are retrofitted with the intrusion alarm systems. Although these systems are primarily intended to detect breech and illegal entry, these can also detect entrants at the open building entrances.
Security sensors, which detect a change of state when a door or window has been opened during an unauthorized time, or in some other unauthorized conditions, have routinely been used as part of alarm systems. Intrusion of a door or window can be detected by a break in an electromagnetic circuit using a device, such as a reed switch, installed in one portion of the window or door and a magnet installed in an adjacent position in the other corresponding portion of the window or door. A typical retrofitted wireless window alarm kit comprises a sensor assembly mounted visibly on the door frame and an actuation element (typically a magnet) mounted on the window flush with the sensor assembly when the window is closed.
U.S. Pat. No. 7,081,816 discloses a wireless security sensor system with a wireless sensor assembly adapted to be retrofitted into a hollow interior of a window or door frame. An actuation unit in the form of a magnet assembly is inserted flush with the sensor into the hollow interior of the corresponding window or door. The sensor and magnet assemblies are hidden within the frame and window, respectively, and thereby not readily seen by an intruder. However, both the sensor assembly and the magnet assembly require 1 inch diameter bore holes in the door/window and in the corresponding frame. Also, a long wire antenna extends from the button shaped assembly housing.
U.S. Pat. No. 5,083,110 discloses a window alarm system with a plurality of small, self-contained thin, elongated units strategically located on a window. The units are either spring-controlled or transducer-controlled, and are set to activate an alarm upon the application of a predetermined amount of pressure thereto, e.g. when an intruder presses/touches one of the self-contained units. This type of alarm is not activated upon movement of a window/door.